It sounds like you mean individual stalks of wheat, or small bunches. I think you might take a look at some of the piping tutorials on wilton.com, it seems to me there might be a picture of wheat. The thing that's coming to mind is doing the Lily of the Valley (I think) where you have a long stem or stalk and little flowers that appear to hang from it. For wheat I would try using a small round tip (3 maybe) and making stems or stalks then use a leaf or petal tip to make the seeds.